PWFS can also vignette the beam - the PWFS can reach an outer radius = 7 arcmin before one edge of their field starts to be vignetted (the 14 arcmin diameter is slightly larger than the instrument FOV because the PWFS are upstream of the Science Fold and ISS ports). Limiting factors on FOV are the diameter of the central openings of the WFS mounting rings in the WFS, the portholes in the ISS, and the Science Fold Mirror diameter. Plate Scale at Cassegrain: 1.610 arcsec/mm.įield of View at Instrument Focal Plane: Maximum 10 arcmin diameter on the bottom port, and 7 arcmin diameter on the side ports due to science fold mirror size. Science Fold Mirrors: These are plane mirrors at 45 degrees that reflect the converging beam near the Cassegrain focus of each telescope to an instrument mounted on one of four side-looking ports of the Instrument Support Structure (ISS) or may be retracted to allow the beam to reach the up-looking instrument on the bottom port of the ISS.Įffective Focal Lengths of Telescopes at Cassegrain Focus: 128.12 m (f/16). The chopping capabilities are: any position angle on the sky at frequencies up to 3 Hz amplitudes up to 15 arcsec on the sky and a duty cycle of 87% at the above values. Tip-tilt correction is possible up to 200 Hz. Each secondary mirror is mounted on a rapid tip-tilt and chopping mechanism designed and built by Lockheed. The rms surface accuracies are 17 nm for the Gemini N mirror and 13 nm for the Gemini S mirror. Each was prefabricated by Schott from Zerodur and then polished by Zeiss to a convex hyperbolic shape and lightweighted by 85%. Secondary Mirrors: Each secondary mirror is 1.0 m in diameter. The measured surface accuracy is 15.6 nm (rms). Each mirror blank was then shipped to REOSC Optique in Paris, France, for polishing of its reflecting surface to that of a concave hyperboloid. Each was made from 55 blocks of low expansion (ULE-581) glass fused together at 1700 degrees C and slumped at Corning's Canton, New York facility. Primary Mirrors: Each mirror is an f/1.8, 8.1 m diameter, 20 cm thick meniscus, and weighs 22,200 kg. Telescope Prescriptions: GN Zemax model | GS Zemax model (GN=MK/Mauna Kea and GS=CP/Cerro Pachon). Telescope Optical Configuration: Ritchey-Chretien Cassegrain. It is useful to understand the ISS position in relation to the telescope when parked at Zenith (it is underneath), and the telescope position on the observing floor, and mount. The instrument specifications webpage provides detailed information relevant to ISS-mounted instruments including interfaces and environmental conditions. The ISS is attached to the telescope via the Cassegrain rotator, which may be oriented at any desired position angle and which normally rotates during observations to compensate for rotation of the field of the alt-az telescope. A science fold mirror mounted inside the ISS can be rotated to send the light from the telescope to any of four side-looking ports, or can be retracted so that the light goes to the up-looking port. The ISS is a stiff cube that itself houses the Acquisition and Guidance Unit which contains the Acquisition Camera and Peripheral Wavefront Sensors (guiders). Instruments are mounted at the Cassegrain focus on the instrument support structure (ISS). Instrument support structure at Gemini South (as of January 2011)
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